Solder flux composition

ABSTRACT

A fluxing composition suitable for soldering electrical connections and characterized by producing a bright and shiny solder joint comprising about 40 to 99 percent by weight of polypropylene glycol and 0.25 to 15 percent by weight phosphoric acid. An optional component in the fluxing composition is 0 to 50 percent by weight rosin.

United States Patent [1 1 Goldfarb et al.

[4 1 Feb. 12, 1974 1 SOLDER FLUX COMPOSITION [22] Filed: Apr. 18, 1973[21] Appl. No.: 352,146

Related U.S. Application Data [63] Continuation of Ser. No. 201,135,Nov. 22, 1971,

abandoned.

[52] U.S. Cl. 148/23, 260/635 [51] Int. Cl. B23! 35/34, C07c 31/20 [58]Field of Search 148/23, 22; 260/635 [56] References Cited UNITED STATESPATENTS 2,992,949 7/1961 Melchiors 148/23 3,436,278 4/1969 Poliak 148/232,664,371 12/1953 Snell 148/23 2,547,771 4/1951 Pessel 148/23 3,175,9323/1965 Brady I 148/23 2,829,998 4/1958 148/23 4/1971 Becker 148/232,801,196 7/1957 Doerr 148/23 3,003,901 10/1961 Marcell..... 148/231,663,004 3/1968 Green 148/23 3,330,028 7/1967 Elbreder 148/23 FOREIGNPATENTS OR APPLICATIONS 1,007,039 10/1965 Great Britain 148/23 OTHERPUBLICATIONS Poliak & Rausch, IBM Technical Disclosure Bulletin (July,1970).

Primary Examiner-Charles N. Lovell Assistant Examiner-Peter D. RosenbergAttorney, Agent, or Firm-11. Fredrick Hamann; G. Donald Weber, Jr.

[57] ABSTRACT A fluxing composition suitable for soldering electricalconnections and characterized by producing a bright and shiny solderjoint comprising about 40 to 99 percent by weight of polypropyleneglycol and 0.25 to 15 percent by weight phosphoric acid. An optionalcomponent in the fluxing composition is 0 to 50 percent by weight rosin.

5 Claims, N0 Drawings SOLDER FLUX COMPOSITION This is a continuation ofapplication Ser. No. 201,135 filed Nov. 22, 1971 and now abandoned.

FIELD OF THE INVENTION This invention relates to soldering fluxes andmore particularly to fluxing compositions containing polypropyleneglycol.

BRIEF DESCRIFTION OF PRIOR ART One of the primary problems with priorart flux composition is the splattering of the flux and/or solder whichis caused by the violent volatilization of the flux composition whenheated. Many commercially available solder fluxes utilize vehicleshaving low boiling points such as water, isopropyl alcohol, turpentineand the like. These low boiling vehicles volatilize below the meltingtemperature range of the soft solders commonly used, that is 120 to310C.

Another problem encountered with flux compositions is the tendency toleave a corrosive residue on electrical connections. The residues areformed when the flux vehicle vaporizes during the soldering steps. Suchresidues tend to promote electrolytic corrosion between the solder andthe metal and may thus cause ultimate failure of the joint underunfavorable atmospheric conditions. Furthermore, in many cases it isdifficult and impractical to wash or otherwise remove the flux residue.As a result, considerable effort has been made to provide fluxcompositions that leave noncorrosive residues or no residues at all orresidues which can be readily removed by washing with organic solventsand/or water.

SUMMARY OF THE INVENTION It is a primary object of this invention toprovide an improved flux composition for soldering.

It is another object of this invention to provide a substantiallysplatter-free flux composition.

It is still another object of this invention to provide a fluxcomposition which remains substantially liquid during the soldering stepthereby facilitating its removal.

These and other objects of this invention are provided by a fluxingcomposition comprising 40 to 99 weight percent polypropylene glycolhaving a molecular weight range between 400 to 4,000, 0.25 to 15 weightpercent phosphoric acid having sufficient water removed so as not toboil between a temperature of between l20 to 310C, and to 50 weightpercent rosin. This fluxing composition is substantially free ofsplattering during the soldering operation, remains liquid after thesoldering operation thereby facilitating its removal from the solderedconnection and produces a bright and shiny solder joint which issubstantially free of imperfections including gas pockets or airinternal voids.

DETAILED DESCRIPTION OF THE EMBODIMENT In general, this invention coversfluxing compositions containing 40 to 99 percent by weight of apolypropylene glycol having a molecular weight range between 400 to4,000, 0.25 to 15 percent by weight phosphoric acid and 0 to 50 percentby weight rosin.

Polypropylene glycol is sold commercially as 1,2- propane-diol. Theaverage molecular weight range is from 400 to 4,000. These polypropyleneglycols have a boiling point of decomposition at temperatures from 300to 450C. The viscosities of these polypropylene glycols range frombetween to 1150 cenistokes at 25C. The polypropylene glycols used inthese fluxing compositions are non-toxic, substantially nonhygroscopicand remain liquid within the melting temperature range of to 310Ccommonly found for soft solders. The preferred concentration range ofpolypropylene glycol is 55 to 80 weight percent.

The phosphoric acid component is ortho phosphoric acid in whichsufficient water of hydration is removed therefrom so that nosplattering of the fluxing composition or solder results therefrom.Typically, commercially available ortho phosphoric acid contains about86 percent ortho phosphoric acid and 14 percent water as water ofhydration. In a preferred embodiment, the commercially available orthophosphoric acid containing 86 percent ortho phosphoric acid is mixedwith the polypropylene glycol and heated to a temperature of about C.During this heating step, some of the water of hydration is removed. Thepreferred concentration of phosphoric acid is 3 to 7 weight percent whenphosphoric acid is the only active component in the flux composition.When phosphoric acid and rosin are used in combination, the preferredconcentration of phosphoric acid is 1 to 3 weight percent and thepreferred concentration of the rosin is 20 to 40 weight percent.Concentrations of phosphoric acid higher than 10 percent tend to darkenthe color of the fluxing solution. Fluxing compositions containing 10 to15 percent orthophosphoric acid are dark colored and tend to leave adark residue on the solder joint. These fluxing compositions will work,however, having the aforementioned disadvantage of a dark residue.

In some applications it is desirable to include the rosin as a componentalong with orthophosphoric acid in the fluxing composition. F luxingcompositions which are rosin free can be readily removed by washing withwater. Fluxing compositions containing rosin yield a residue which isremoved by washing with organic solvents.

The fluxing composition removes the oxide film from the metal to besoldered. At the same time, the fluxing composition protects the-solderduring the soldering operation to produce a bright shiny solder jointwhich is substantially free of internal gas pockets. The fluxingcomposition is substantially free of low-boiling solvents and hence doesnot cause any splattering during the soldering operation. The flux is aliquid and remains so during and after the soldering step. The liquidflux residue can be readily removed by washing with water or an organicsolvent.

EXAMPLE 1 A mixture containing 97 grams polypropylene glycol having amolecular weight of 1010 and 3 grams of or- Polypropylene Example No.Ortho Rosin Wt. 7:

Glycol, Wt. Phosphoric Acid, Wt.

We claim:

1. A non aqueous, liquid fluxing composition which is non splatteringduring soldering consisting of about 40 to 99 percent by weight ofpolypropylene glycol having an average molecular weight of 400 to 4,000and which is non-volatile during said soldering,

about 0.25 to 15 percent by weight orthophosphoric acid which issufficiently dehydrated to enable said composition to be substantiallysplatter free during soldering, and

the balance about 0 to 50 percent by weight of rosin.

2. A fluxing composition as described in claim 1 wherein the averagemolecular weight of said polypropylene glycol is between 700 and 1,500.

3. A fluxing composition as described in claim 1 wherein theconcentration of said ortho phosphoric acid is 3 to 7 weight percent andthe concentration of the rosin is 0 weight percent.

4. A fluxing composition as described in claim 1 wherein theconcentration of the ortho phosphoric acid is l to 3 weight percent andthe concentration of the rosin is 20 to 40 weight percent.

5. A fluxing composition as described in claim 1 wherein theconcentration of the polypropylene glycol is 72 to 76 weight percent,the concentration of the ortho phosphoric acid is 0.5 to 2 weightpercent and the concentration of the rosin is 24 to 26 weight percent.

2. A fluxing composition as described in claim 1 wherein the averagemolecular weight of said polypropylene glycol is between 700 and 1,500.3. A fluxing composition as described in claim 1 wherein theconcentration of said ortho phosphoric acid is 3 to 7 weight percent andthe concentration of the rosin is 0 weight percent.
 4. A fluxingcomposition as described in claim 1 wherein the concentration of theortho phosphoric acid is 1 to 3 weight percent and the concentration ofthe rosin is 20 to 40 weight percent.
 5. A fluxing composition asdescribed in claim 1 wherein the concentration of the polypropyleneglycol is 72 to 76 weight percent, the concentration of the orthophosphoric acid is 0.5 to 2 weight percent and the concentration of therosin is 24 to 26 weight percent.